This is a double-blind, placebo-controlled trial that will contrast the effects of a soy dietary supplement (a rich source of the plant estrogen genistein [l mg/g protein] and protein) with the effects of conjugated equine estrogens on measures of health and quality of life in perimenopausal/menopausal women. We will randomize perimenopausal women (45-55 years of age) into one of three groups (placebo, conjugated equine estrogens, or soy supplementation). The specific aims of the study are: 1) to determine the impact of the interventions on menopausal complaints (i.e., hot flushes, mood lability, anxiety, sleep disturbances); 2) to assess effects on plasma lipids and lipoproteins, including lipoprotein (a); 3) to monitor interventional effects on vaginal bleeding and endometrial proliferation; and 4) to evaluate changes in health-related quality of life. Secondary endpoints will include assessment of the impact of these interventions on: 1) the progression of carotid artery intimal medial wall thickening as assessed by B-mode ultrasonography; 2) bone density and bone turnover; and 3) additional measures to monitor the compliance and safety of the intervention such as mammography, anticipated or known side effects of hormone replacement therapy, blood levels of genistein, and clinical outcomes (hospitalizations, physician visits, and symptoms). This project will involve the collaborative efforts of a multidisciplinary team with substantial expertise in the areas of controlled clinical trials, gynecology, health-related quality of life, cardiovascular disease, biostatistics, nutrition and osteoporosis. A strength of this project is its parallel design with the nonhuman primate trial. This will enable an overall evaluation of the efficacy of dietary soy supplementation through comparisons between the symptoms and disease outcomes, and the direct effects on the appropriate organ systems as determined by physiologic and histopathologic measurements in nonhuman primates.